1. Technical Field
The present invention relates to a liquid crystal display and a driving method, and more particularly to a liquid crystal display and a driving method that adaptively controls the brightness of a backlight.
2. Description of the Related Art
Liquid crystal display devices control a light transmittance of liquid crystal cells in accordance with a video signal and display a picture. Liquid crystal display devices having a switching device formed at each cell are referred to as an active matrix type.
FIG. 1 schematically shows a liquid crystal display device 10 of an active matrix type in the related art. In FIG. 1, the liquid crystal display device 10 includes a system 17, a liquid crystal display panel 15, a backlight 16, a data driving circuit 13, a gate driving circuit 14, a timing controller 12, an interface circuit 11, a DC-DC converter 18, and an inverter 19. The system 17 includes an electronic device which uses the liquid crystal display device 10 for a display. The liquid crystal display panel 15 has m×n number of liquid crystal cells Clc which are arranged in a matrix type, m number of data lines D1 to Dm and n number of gate lines G1 to Gn which cross each other, and a thin film transistor (hereinafter, referred to as “TFT”) which is formed at the crossing.
The backlight 16 irradiates a light to the liquid crystal display panel 15. The data driving circuit 13 supplies data to the data lines D1 to Dm of the liquid crystal display panel 15. The gate driving circuit 14 supplies a scanning pulse to the gate lines G1 to Gn. The timing controller 12 controls the data driving circuit 13 and the gate driving circuit 14. The interface circuit 11 is connected between the system 17 and the timing controller 12. The DC-DC converter 18 generates driving voltages of the liquid crystal display panel 15. The inverter 19 drives the backlight 16.
The liquid crystal display panel 15 has a liquid crystal formed between two glass substrates. On the lower glass substrate of the liquid crystal display panel 15, the data lines D1 to Dm and the gate lines G1 to Gn intersect each other. Each intersection between the data lines D1 to Dm and the gate lines G1 to Gn is provided with the TFT. The TFT supplies data on the data lines D1 to Dm to the liquid crystal cell Clc in response to a scanning pulse from the gate lines G1 to Gn. To this end, the gate electrode of the TFT is connected to the gate lines G1 to Gn while the source electrode of the TFT is connected to the data line D1 to Dm. Further, the drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc.
A graphic processing circuit of the system 17 converts an analog data into digital video data RGB and, at the same time adjusts a resolution and a color temperature of the digital video data RGB. The digital video data RGB is supplied, via the interface circuit 11, to the timing controller 12.
The interface circuit 11 may use a TMDS (Transition Minimized Differential Signal) method or a LVDS (Low Voltage Differential Signaling) method. The TMDS method converts a digital video data into a TTL level or a CMOS level and transmits the converted video data in parallel. The LVDS method compresses the digital video data RGB in serial data, transmits the compressed serial data and then restores the compressed serial data to parallel data. Accordingly, a frequency and a voltage of the digital video data RGB may be smaller, and the number of signal line that transmits the digital video data RGB also may be reduced.
FIG. 2 illustrates a backlight control method using an average brightness of input digital video data RGB for use with the liquid crystal display device 10. The average brightness of digital video data RGB for each frame unit is calculated and the brightness of the backlight 16 is controlled in accordance with the average brightness. As a brightness range of an image signal increases, the liquid crystal display device 10 may produce a clear image by use of the backlight control as shown in FIG. 2.
The liquid crystal display device 10 depends solely on the average brightness of the input digital video data RGB to adjust the brightness of the backlight 16 and realize a clear image. The liquid crystal display device 10 may not substantially consider picture quality perception of a user in accordance with a change of an external environment, and an image property.
For instance, a user may perceive the contrast of an image differently due to a change of the external illumination. When the external illumination is low, although the backlight 16 is less bright than the average brightness of input digital video data RGB, a user may perceive that the contrast of the image is high. On the contrary, when the external illumination is high, the brightness of the backlight 16 should be brighter than the average brightness of input digital video data RGB and a user perceives the image as having a high contrast. Accordingly, information on the average brightness of the input digital video data RGB alone may not allow for an accurate evaluation of an image contrast.
Additionally, a preference for a certain level of contrast may be different depending upon the type of an image. For instance, an image corresponding to sports such as tennis normally may require a higher contrast than an image corresponding to movies. However, a certain user may prefer to watch the movies with higher contrast. Accordingly, there is a need for a liquid crystal display device that overcomes drawbacks of the related art.